The invention relates to a stamping press and in particular to a transfer press having means for enabling the upper and lower dies to be changed quickly.
In producing parts by stamping, it is often necessary to perform a number of successive individual stamping operations in progressing from strip stock or blanks to the finished product. As an alternative to performing each stamping operation on a separate press or on the same press following a die change, press systems have been developed whereby a plurality of successive stamping operations can be performed in one pass through a single press.
One such system employs a die arrangement called a progressive die wherein the workpiece starts as a strip of stock and progressively assumes the desired final shape as it passes through the die stations in succession. In a progressive die, the workpiece remains attached to the edge portions of the strip so as to facilitate locating of the workpieces in the various die stations. Although accurate locating of the workpiece is simplified, the necessity that the workpiece be attached to the edge of the strip restricts the type of stamping operations which can be performed.
A press system which overcomes some of the drawbacks inherent in progressive die systems is the transfer press. In this machine, individual blanks or pre-formed parts are loaded into the press and then advanced successively from die station to die station by means of feed bars having part engaging fingers attached thereto. On the upstroke of the press, the bars and fingers move inwardly, grip the partially formed workpieces in each die station, lift if necessary, and advance them to the next stations for further forming on the downstroke of the press. The primary drawbacks to both the progressive die system and transfer press is, firstly, the extremely high cost of the die sets and, secondly, the considerable length of time required to change dies. In the case of a transfer die, for example, it often requires as long as one day to one day and a half to change the die sets which results in costly machine down time. For these reasons, progressive dies and transfer dies are economically feasible only for very large runs. In times of economic uncertainty, however, most part orders are relatively small, and the inordinately long press down time necessitated by die changing cannot be justified.